1. Field of the Invention
The present invention relates to a battery cooling structure in which a large number of rod-shaped battery modules are arranged in parallel to each other at predetermined intervals within a battery case, and these large number of battery modules are cooled with cooling air.
2. The Related Art
Japanese Patent Application Laid-open Nos. 10-255859 and 11-329518 disclose an arrangement in which a long rod-shaped battery module is formed by connecting a plurality of battery elements together in series, and a large number of the battery modules are arranged in parallel to each other at predetermined intervals within a battery case, the arrangement being employed as an energy source for a motor for travel of an electric automobile. Since these battery modules generate heat during charging and discharging, cooling is carried out by passing cooling air from a cooling air inlet at the front end of the battery case to a cooling air outlet at the rear end. Since the plurality of battery modules are arranged in multiple vertical rows and multiple tiers, and the cooling air flows from a front vertical row to a rear vertical row, the battery modules on the front vertical row side are cooled efficiently by contact with low temperature cooling air that has not yet carried out heat exchange, but the battery modules on the rear vertical row side contact cooling air whose temperature has been increased by heat exchange, so that they have difficulty to be cooled. In particular, among the battery modules on the rear vertical row side, the cooling effect to the battery modules in a middle tier, which are far from an inner face of the battery case, is degraded. In this way, the difference in cooling effect causes a variation in the temperature of the battery modules, leading to a problem that the capacity decreases or the durability is degraded.
In the arrangement disclosed in Japanese Patent Application Laid-open No. 10-255859, low temperature cooling air is replenished by connecting a bypass passage to a middle part, in the direction of flow of cooling air, of the battery case, and in the arrangement disclosed in Japanese Patent Application Laid-open No. 11-329518, the variation in the temperature is eliminated by replenishing low temperature cooling air via an opening formed in a middle part, in the direction of flow of cooling air, of the battery case so as to uniformly cool the battery modules on the upstream side and on the downstream side in the direction of flow of cooling air.
However, providing the bypass passage for introducing the cooling air gives rise to a problem that the structure of the battery case becomes complicated or the dimensions thereof increase, and providing the opening for introducing the cooling air also gives rise to a problem that the layout of the battery case is restricted in order not to block the opening.